Thermal spraying is a process of melting and propelling fine particles of molten material such as metal to form a coating. One type of thermal spray gun is a dual wire, arc thermal spray gun in which two wires are fed into electrical contact at the wire ends. The ends are melted by an electrical arc with current passed through the wires. A jet of compressed gas (usually air) is blown through the tips to atomize (i.e. nebulize) the molten metal and effect a spray stream of molten metal particles. Arc current generally is of the order of hundreds of amperes. Typically the power is brought through cables connected to feed rollers and/or wire guides in the gun that electrically contact the wires and guide them to the point of arcing.
Various configurations for jetting the atomizing air to the melting wire tips have been used in efforts to provide an effective spray stream, and for introducing auxiliary air to modify and improve the spray stream, for example as taught in U.S. Pat. No. 4,668,852 (Fox et al.) However, there has remained a need for improvement in the spray stream, particularly for a higher velocity, narrower spray in order to decrease oxidation of the atomized particles in transit for improved coating quality and deposition efficiency. As atomization in a gun may be satisfactory, it is desirable to improve the spray stream without affecting the arc or the atomization.